3GPP has defined the Policy and Charging Control (PCC) feature to allow the QoS (Quality of Service) control and differentiated charging per service data flow. The latter is defined as the user plane packets in the access that match a certain PCC rule.
A separate node, the Policy and Charging Rule Function (PCRF) is responsible for activating the appropriate PCC rule for each access. The PCRF can provide a dynamic PCC rule to the GGSN/PDN-GW (Gateway GPRS Support Node/Packet Data Network Gateway) over the Gx reference point in the 3GPP architecture. The GGSN/PDN-GW may host predefined rules, which may include more advanced detection capabilities than what is possible with dynamic rules. Still the PCRF can, by referencing the rule by name, activate and deactivate the rule for a certain user.
The 3GPP Rel-8 architecture is illustrated in FIG. 1. The architecture will not be described in detail here. Further information regarding the architecture can be received by studying this 3GPP project.
The service data flow detection at the GGSN/PDN-GW is local in that node. The result of the service data flow detection is not communicated in the user plane outside the GGSN/PDN-GW. With the 3GPP Re.-8 architecture, there are deployment options (variations of Mobile IP—MIP) where a single (MIP) tunnel conveys the traffic between the PDN-GW and (e.g.) the Serving GW (S-GW).
The 3GPP Rel-8 non-roaming architecture for PMIP-based (Proxy MIP) access is shown in FIG. 2. The architecture will not be described in detail here. Further information regarding the architecture can be received by studying this 3GPP project.
Reference point Gx in FIG. 2 is the same as Gx in FIG. 1, the Gxc reference point corresponds to Gxx, which has got the name settled to be Gxx. In FIG. 2, the PCEF (Policy and Charging Enforcement Function) is located in the PDN-GW and the BBERF (Bearer Binding and Event Reporting Function) in the S-GW.
From the S-GW towards the UE, (see FIG. 2) there are bearers, with differentiated QoS, to which the S-GW is expected to map the service data flow according to the PCRF policy decision. For that purpose the PCRF provides, for dynamic rules, the rule that is necessary (a.k.a. QoS rules) to do the service data flow detection and the proper mapping to downlink bearers at the S-GW.
Since the predefined rules, when using capabilities beyond dynamic rules, cannot be provided to the S-GW from the PCRF, it is not possible to conduct PCC control over such traffic at an S-GW (in the MIP deployment scenarios) with a solution based solely on 3GPP Rel-8 standard. This also implies that any kind of application level policies per bearer in the S-GW (BBERF), e.g. application level access control or policing, would be impossible.
In order to achieve this, extensions would be required to the standard functionality. One possible solution to the problem is to duplicate both the predefined rules as well as the actual detection (may be arbitrarily complex) at both the PDN-GW and the S-GW. But this is disadvantageous for several reasons:                Performing classification of pre-defined services by the use of so called deep-packet inspection (DPI) in the S-GW will severely impact the performance of the S-GW. This implies an increased need for processing power and this will eventually lead to increased CAPEX (Capital Expenditures) for the operator.        DPI is performed redundantly for each packet (once at the PCEF and then once more in the S-GW) introducing highly unwanted latency into the user plane.        Pre-defined rules in S-GW must be aligned with the ones in the PCEF. Apart from the obvious O&M implications this will have on an operators own network (i.e. increased OPEX—Operational Expenditures), this will practically preclude the use of home routed access for the roaming case.        
To summarize, the current 3GPP EPC (Evolved Packet Core) architecture (formerly known as SAE—System Architecture Evolution) does not provide the adequate means to perform downlink bearer binding based on pre-defined rules when the bearer binding function is located in the S-GW (BBERF). Currently only dynamically provisioned QoS rules provided by the PCRF can be used for this. A non-standardized solution that duplicates the packet inspection mechanism in the S-GW is expensive and quality degrading.